Method of making elastic polyurethane filamentary material using tertiary nitrogen-containing catalyst



June 29, 1965 c. v. TALLMAN ETAL.

METHOD OF MAKING ELASTIC POLYURETHANE .'FILAMENTARY MATERIAL USING TERTIARY NITROGEN-CONTAINING CATALYST Filed March 21, 1965 United States Patent O METHQD OF MAKING ELASTIC POLYURETHANE FILAMENTARY MATERIAL USING TERTIARY NITROGEN-CONTAINNG CATALYS'I Charles V. Tallman and Gus D. Keritsis, Gastonia, N.C., and Robert A. Gregg, Kinnelon, NJ., assignors to United States Rubber Company, New York, N.Y., a corporation of New Jersey Filed Mar. 21, 1963, Ser. No. 266,992.

Y7 Claims. (Cl. 264-184) This invention relates to a continuous, high-speed method `of making iilamentary material, and more particularly it relates to a method of making elastic polyurethane thread or liber, as well as to -improved thread made by such method. i

The invention is base upon the discovery that usually rapid cure of a polyurethanevthread made from a liquid polyurethane prepolymer can be accomplished, in such 3,192,296 Patented June 29, 1965 ICC nitrogen-containing organic catalyst. Build-up of modulus in the water cure step when this procedure is followed is several fold that obtained if the tertiary nitrogencontaining catalyst is added in either the coagulation (diamine setting) or the water-cure stages of the process. The invention will be described with reference to the accompanying drawing, wherein:

FIG. .1 is a schematic diagram showing one method of practicing the invention; and, FIG. 2 is a cross-sectional view, on an enlarged scale,

Y of an elastic thread made in accordance with the invena manner as to provide a thread of excellent quality, by

contacting the thread, subsequent to an initial setting of the thread in a diamine bath but prior to a final cure of the thread in water, with an organic compound containing a tertiary nitrogen atom.

In one aspect, the invention is an improvement upon the polyurethane thread and method of making same disclosed in U.S. Patents of Kohrn et al., 2,953,839, September 27, 1960, and 3,009,762, November 21, 1961, and application Serial No. 182,001, iiled March 23, 1962, by R. A. Gregg and C. V. Tallman, now U.S. Patent 3,111,- 369, November 19, 1963. The patents referred to described making a poly urethane thread or filament from a polyurethane prepolymer, which is a reaction product of a hydroxy-terminated polyester or polyether or the like with an organic diisocyanate. Such prepolymer is extruded into an aqueous solution of an aliphatic diprimary diamine to coagulate the thread, that is, to cause a rapid setting or gelling of the surface of the thread. Subsequently, cure of the thread is completed by the action of Water. The copending application referred to deals with the improvement of having a monoalcohol or glycol present in the setting bath to improve Y the setting action. 4

Unfortunately, if it is attempted to speed up the water cure of the thread by adding certain catalytic materials to the water in which the thread is conventionally immersed for final cure, there is a tendency for the thread to suffer hydrolytic degradation coincident with cure. This is evidenced by a progressive falling oii in the tensile properties of the thread as the catalyst concentration in the cure bath is increased. Also, there is an undesirable tendency for thread cured in water containing a catalyst to exhibit blowing or similar discontinuities occasioned by too rapid formation of carbon dioxide (a normal byproduct of the curing reaction of water on polyurethane) in the thread during the cure. Furthermore, the rates of cure achieved when certain catalytic materials are put directly into the iinal Water cure bath are frequently not as high as would be desirable.

We have now found that the foregoing disadvantavgeous can be overcome, and additional advantages which will be made manifest hereinbelow can be realized, by

tion.

Referring to the drawing, one method of practicing the invention, a liquidpolyurethane prepolymer which is contained ina suitable supply tank 10 is extruded in the form of a tine stream through'a nozzle 11 having a circular orifice into a bath of coagulating or setting liquid 12, in the conventional manner. The composition of the polyurethane prepolymer is conventional and requires no detailed exposition here. It may bedescribed as an isocyanate-terminated, uncured polymer which is a reaction product of an hydroxy-terminated polyester or polyether with an excess of an organic diisocyanate. Reference may -be had to the aforementioned patents and application, the disclosures of which are hereby incorporated herein by reference, for more detailed description of the prepolymer as well as the `setting bath, which is based on an aqueous solution of an aliphatic diprimary diamine. It will be understood that the setting or coagulating bath causes an initial setting or solidiiication of the cylindrical stream of liquid prepolymer, as it enters the bath, converting it into a thread 13 which can be handled as a solid through subsequent steps of the process. A driven spinning roller 14 controls the rate of advancement of the freshly coagulated or initially set thread 13 away from the extrusion nozzle 11, and to avoid imposing excessive straining forces on the thread, which is soft and delicate in the initially set and uncured state, a positive conveying device, such as a series of driven rollers 15, 16, 17, etc., guides and advances the thread through subsequent stages of the process to be described below. Asis disclosed in more detail in application Serial No. 182,001, now Patent No. 3,111,369, referred to previously, the setting bath typically includes 5 to 90% (preferably 20 to 70%) by weight of a monoalcohol having l to 8 carbon atoms, a glycol having 2 to 10 carbon atoms, or a mixture thereof (e.g. alkanols such as npropanol, tertiary-butyl alcohol, ethyl Carbitol, butyl Cellosolve, ethylene glycol, hexylene glycol, and the like).

From the coagulati-ng bath the moving filament is passed through a rinse bath 24 of Water to remove excess coagulant.

The thread next passes, in accordance with the invention, into a catalyst bath 2 which comprises an organic compound having a tertiary nitrogen atom. Suitable catalytic materials, capable of catalyzing the curing reaction 'of water with polyurethanes, are tertiary amines or heterocyclic compounds containing at least one ring tertiary nitrogen, and include the following:

(l) Tertiary alkyl amines, for example triethyl amine and N,N,N,Ntetramethyl1,3-butanediamine.

(2) Pyridine `and substituted pyridines such as alkyl, halogeno- -or amino-pyridines, for example, 2,4-lutidine and 2-chloro-pyridine. Similarly, quinoline and correspondingly substituted quinolines.

(3) 1-a1kyl-morpholines, for example, l-ethylmorpholine and 1,1ethylenedimorpholine.

(4) Alkyl-imidazoles, for example, Z-methylimidazole and 1,2-dimethylimidazole.

(5) Alkylor amino-piperazines,v for example, 1,4-di-Y methylpiperazine, l,2,4-trimethylpiperazine and N-(betaaminoethyl)piperazine.

(.6) 1-alkyl-pyrroles and -pyrrolidines, for example, N- methylpyrrole and N-methylpyrrolidine.

(7) Pyrazine and alkyl-pyrazines, for example, 2V-meth-V Chemicals of the foregoing kinds in which any alkyl groups are lower alkyl groupsy (eg, 1-4 carbon atoms) may be mentioned particularly.

Conveniently the foregoing catalytic substances are used in the form of a solution, although with suitableV equip` ment they may be applied from vapor phase. When ap plicationfis from `solution Water is usually employed as catalyst possesses low interfacial tension with both the' polyurethane and the Waterused for cure. The catalyst desired to a final washing and .curing bath 33 of water which may be .the hottestof the series (eg, almost boild ing) and in which the Wash water is essentially pure (i.e., catalyst-free) because virtually all of the Water-extractJ able catalyst hasby this time been removed. The treat ment is thus countencurrent in the sense that the thread progresses inthe direction of increasing'temperature and increasingpurity of the Washing and curing Water. In this last :bath the water-cure lof the threadfbecornes so far advanced that the thread, after running through a bath 35 of textile lubricant (silicone emulsion) and being Wound up in a package 37, isafterlstanding 24 hours or so, virtually completely cured,` although there is usually no denite end-point to the cure and changes in physical propertiesrnayin` some cases continue for a period of days, particularly by virtue of the `action'of `moisture re Y maining in the thread and/or moisture absorbedfrom employed (or combination of catalysts) is soluble, both action desired, and other conditions prevailing in the process. Usually the concentration of catalyst is at least 20% by Weight of the bath, ranging up to 80 or 90% or even higher (to- 100%), with the more usual concentrations being in the range of Sli-80%. The catalyst bath can beemployed at room temperature but it is preferably heated slightly to a range of 90-130 F. for example. The contact of the thread with the catalytic bath is very brief. In `many cases a contact time as little as one second is more than suliicient to sensitize the thread ap preciably to the action of the subsequent Water cure. Somewhat longer contact times are more usual, say 2 to 8 seconds, but in any event it is not necessary to contact the thread with the catalyst for .appreciably longer periods than l0-20 seconds. the catalytic bathy containing Va tertiary-nitrogen organic compound, a small but effective amount of the catalytic material diffuses into or is dissolved in the uncured thread and is carried along with the thread as thelatter'leaves the catalyst bath 25.`

In accordance with an important feature of the present invention, the thread is removed from the catalyst bath for completion of the cure by the action of Water after the excess catalyst has been washed olf .the thread. By arranging the Water cure so that the thread is exposed to a succession of conditions such that the temperature and purity (i.e., freedom from catalyst) of the water are in creased as the cure progresses, rapid `build-up of cure Vand thorough Wash-out of catalyst are accomplished concurrently. Thus, after leaving the catalyst bath 25, the thread may pass into a lirst Washing and curing bath 27 of water heated to a relatively moderate temperature of, for example, 140-1 60 F. to remove the bulk of the excess catasV As a resultvof such contact with f lyst from the surface of the thread :and to start the waterfk l .curing of the thread. The thread next passes -intoa sub-` l the air'. It Will be understood that, if the conditions in the successive Washing and curing baths (particularly with respect to temperatures employed and duration of exposures to the baths) are not such as to bring the cure to a substantiallyY .completed stage, vthe package ofthread may if desired be' immersedV in hot water (suitably in an autoclave) to Acomplete the'cure.YAY

As mentioned previously,.carbon dioxide gas is normally evolved asaresult of the reaction-of water with polyurethane. In-conventional lpractice this gives rise to diiiiculties because the evolved gas tends to produce voids or` other discontinuities in they thread. Such dirhculties are particularly Ilikely to occur if itis attempted to carry out the cure rapidly, by. previously known methods. However, it is an important feature-of the present invention that the tertiary-nitrogen-containing catalyst which is present within the lthread Whenit entersVr the'y rst stage of cure actsl to hold thefcarbon dioxide in the dissolved state. This dissolved 4carbon dioxide, along with Yremaining traces of catalyst, is removed as contact with progressively hotterand cleaner Water is made. When the cure is effected with the individual larnent surrounded by the Water bathas described, ,the gas hask time to diluse out of the ilamentinto' the surroundingwater in which it is soluble. By this sequence bubbleformation, as well as hydrolytic degradation of the polyurethane by the catalyst, are avoided to a remarkable degree, and a given level of cure (as evidenced by developmentof elastic properties andinsolubility) is achievedV much more expeditiously than by prior practice. The final cured thread is accordingly a productlwhich has initially been set or solidified (cross-linked) on its surface by the action of a diamine, and in which the cure (cross-linking) haslbeenrcompleted by the action of Water. Thus the product. 38 ,may be represented as in FIG. 2 as having concentric zones 39.and 40, the outer Zone 359k being .suchthat a substantial part ofthe crosslinking has been accomplished by diamine and the inner vzone 40 being such that the cross-linking has been accomplishcd predominantlyby water. However, it will be understand that there is no deiinite demarcation between the diamine-cured surface and the..water-curedinterior, and the entire thread is probablyin some measure cured partly by both cross-linking agents, diamine and water, because diffusion of` both of the agents probably takes each of them to all parts ofthe thread.

In place of carrying outthe curing process on a running ilament as described, thefthread may instead be Wound up intova package at an appropriate stage-for example, after Washing away the catalyst composition*- and the thread'rnay thereafter be cured batchwise-for example, by immersing the package in Water under pressure at elevated temperature. Any combination of such procedures may beused if desired; for example,V cure of the catalyst-treated thread may be started by running the thread through Warm Water (which also serves to wash out the catalyst), the thread may then bewound up into a package, and such package immersed in water in an autoclave. It will be understood that the contact of the thread with the final cure water need not be by actual immersion in all cases, but may be accomplished, for example, by spraying it with water, or even by subjecting it to steam, particularly in the last stages of the cure when the thread is suiiiciently washed, strong and nonthermoplastic.

We desire to emphasize that it is an important aspect of the invention that the substantially uncured polyurethane thread is sensitized by contact with catalyst subsequent to the initial setting or coagulation of the liquid prepolymer by diamine but prior to substantial advancing of the water-cure. Contact with the catalyst is relatively brief and transitory in comparison with the length of the water curing period. No detectable cure takes place in the catalyst bath when judged by the fact that no increase in gel strength occurs during this step.

By the process of the invention, in which the initially set thread is sensitized by brief contact with a catalyst Comprising an organic compound having a tertiary nitrogen atom, and is then Washed and cured, attainment of i a given level of cure can be accomplished in approximately one-fourth the time, with less risk of bubble formation or hydrolysis, that is required if the catalyst is incorporated in the actual cure water. It is indeed remarkable that a faster, improved cure is achieved by pretreatment of the set thread with catalyst, as opposed to curing the thread in water containing the catalyst. Especially is this true where the aqueous diamine setting bath contains the preferred alcohol and/ or glycol additive.

The following examples will serve to illustrate the invention in more detail.

Example I A polyester having a molecular weight of 2100 and an acid value of 0.7 is prepared by condensing a 70/ 30 mixture of ethylene glycol and and 1,2-propyler1e glycol with adipic acid, the glycol being used in slight molar excess to insure hydroxyl terminal groups. Ten percent of titanium dioxide is dispersed into the polyester, for purposes of pigmentation, by paint-milling. 2310 parts (l mole) of the polyester, containing titanium dioxide, is heated at 55 C. in a glass-lined vessel, provided with a mechanical stirrer, a dry nitrogen inlet-tube, a condenser, and a thermometer. 500 parts by weight (2 moles) of p,p-diphenylmethane diisocyanate is added to the polyester and the mixture is heated to 120 C. Heating is continued at this temperature for 120 minutes. A blanket of dry nitrogen over the reaction mixture keeps out atmospheric moisture. The prepolymer is of white color and has a Brookfield Viscosity of 9500 poises at 85 F.

The prepolymer is extruded at the rate of 3 cc. per minute into a coagulating bath containing 2 parts of ethylene diamine, 1.0 part of a nonionic wetting agent (e.g., methylphenol ethylene oxide condensation product, Triton X- 100), 62 parts of water and 35 parts of n-propanol, maintained at 90 F. The diameter of the nozzle opening is 0.02 inch. The surface of the extruded round stream of liquid sets to a solid condition immediately as it enters the setting bath. A spinning roll rotating at a peripheral speed of 100 feet per minute, located 10 inches from the nozzle, serves to pull the resulting round thread from the nozzle. The thread is immediately rinsed with water to remove the n-propanol, dipped in a pre-sensitizing catalyst bath consisting of 100% N-ethylmorpholine maintained at a temperature of 90 F., laid on a conveyor to allow the catalyst 3 seconds to penetrate, and then carried immediately into a bath of water to be washed and cured. Conditions in the Water bath are regulated so that clean water enters at the far end and passes counter-current to the thread. Temperature of feed water is near the boil and of discharge water near 150 F. Temperature is highest and water cleanest at the termination of the cure. Dwell time in the cure is approximately 30 seconds. n Washing occurs throughout the cure.

The cured thread is run through a lubricating solution of silicone emulsion and wound into a package. Tensile strength at this time is typically 2000 p.s.i. and rises to near Example Il y The same prepolymer as in Example I is extruded at the rate of 5 cc. per minute into a coagulating bath containing 2 parts ethylene diamine, 2 parts of nonionic wetting agent, 56 parts water and 40 parts hexylene glycol maintained at 130 F. The diameter of the nozzle is .024 inch and the spinning roll rotates at a peripheral speed of 75 feet per minute. The pre-sensitizing catalyst bath consists of 4 seconds dwell in 55% N-ethylmorpholine, 20% 1,4-dimethylpiperazine, and 25% water, maintained at 110 F. Dwell time in the first cure under the same conditions as in Example I is approximately 15 seconds after which the thread is lubricated with silicone, and a thin layer of thread is laid on a curing cylinder under substantially no tension. Tensile strength at this stage is typically 200 p.s.i. and lower layers build to near 2000 p.s.i. prior to doif. When between 8 and 16 ounces have been laid on the cylinder, the package is doffed and immersed in water at 120 F. under 50 p.s.i. pressure for an additional 30 minutes. This treatment gives a final wash and results in thread with a uniform tensile of around 10,000 p.s.i.

Example III Example I was repeated using in turn each of the following catalysts to get the listed tensile at take-up:

P.s.i.

2,4-lutidine in water) 3000 N,N,N,Ntetramethylbutanediamine (70% in Water) 1000 Example V In this example, the prepolymer is based on a polyether, polytetramethylene glycol, rather than a polyester. Polytetramethylene glycol having a molecular weight of 2146 is paint-milled with ten percent by weight of titanium dioxide. 2361 grams (1 mole) of the polytetramethylene glycol, containing titanium dioxide, is heated to 60 C. in a 3-necked flask provided with a mechanical stirrer, a dry nitrogen inlet tube, a condenser and a thermometer. 487.5 grams (1.95 moles) of p,pdiphenylmethane diisocyanate is added and the mixture is heated to C.; the heating is continued for minutes. A blanket of dry nitrogen over the reaction mixture keeps out atmospheric moisture. The prepolymer is of a white color and has a Brookfield viscosity of 8250 poises at 100 F. This prepolymer is converted into thread as in Example I. Representative properties are:

v'Tensile strength at windup-1600 p.s.i.; after final cure, tensile- 6000 p.s.i.; elongation-580%; set-30%; 300% massaged modulus-250 p.s.i.

Having thus described our invention, what we claim and desire to protect by Letters Patent is:

1. In a method of making a lamentary material comprising the steps of providing a liquid polyurethane prepolymer having terminal isocyanate groups, extruding a line stream of said liquid prepolymer into an aqueous aliphatic diprimary diamine setting bath to effect an initial setting of the extruded material in' the form of a thread, and thereafter curing the thread by the action of water, the improvement comprising sensitizing said thread, subsequent t0 said initial setting but prior to said water Cure, by contacting the thread With a catalytic material that is soluble in water and soluble in the said prepolymer, and washing the catalyst out of the thread prior to comple-- tion of said cure, the said catalytic material comprising an organic compound containing a tertiary nitrogenatom selected from the group consisting of alkyl tertiary amines, pyridine, alkyl-pyridines, halogeriO-pyridines, amino-pyridines, quinoline, alkyl-morpholines, alkyl-imidazoles, alkyl-pyrroles, alkyl-pyrrolidines, pyrazine, and alky1-pyra zines, the said alkyl groups being lower alkyl groups.

2. YA method as in claim l in which the said setting bath contains an organic solvent selected from the group consisting of monoalcohols having from l to 8 carbon atoms,

glycols having from 2 to l0 carbon atoms, and mixtures thereof.

3. A method as in claim 2 in which at least a rst portion of the Water cure is carried out by Conveying the thread through successive stages of progressively hotter Q o water, whereby the amount of catalyst remaining in the thread becomes progressively less as the cure advances.

4. A method as in claim 3 in which the catalyst comprises N-ethylmorpholine. Y

S. A method as in claim 3 in which the catalyst comprisesy 1,4-dimethylpiperazine.

6. A method as in claim 3 in which the catalyst comprises 2,4lutidine. Y

7.` A method asin clair-n3 in which the catalyst comprises N,N,N,Netetramethylbutanediamine.

Reterences Cited by the Examiner UNITED STATES PATENTS 3,947,356 7/62 Polanskyr 1S-54 ALEXANDER H. BRODMERKEL, Primary Examiner. rvroRRIs HERMAN, Examiner. 

1. IN A METHOD OF MAKING A FILAMENTARY MATERIAL COMPRISING THE STEPS OF PROVIDING A LIQUID POLYURETHANE PREPOLYMER HAVING TERMINAL ISOCYANATE GROUPS, EXTRUDING A FINE STREAM OF SAID LIQUID PREPOLYMER INTO AN AQUEOUS ALIPHATIC DIPRIMARY DIAMINE SETTING BATH TO EFFECT AN INITIAL SETTING OF THE EXTRUDED MATERIAL IN THE FORM OF A THREAD, AND THEREAFTER CURING THE THREAD BY THE ACTION OF WATER, THE IMPROVEMENT COMPRISING SENSITIZING SAID THREAD, SUBSEQUENT TO SAID INITIAL SETTING BUT PRIOR TO SAID WATER CURE, BY CONTACTING THE THREAD WITH A CATALYST MATERIAL THAT IS SOLUBLE IN WATER AND SOLUBLE IN THE SAID PREPOLYMER, AND WASHING THE CATALYST OUT OF THE THREAD PRIOR TO COMPLETION OF SAID CURE, THE SAID CATALYTIC MATERIAL COMPRISING AN 